OBSERVATORY

By HENRY FOUNTAIN

Published: March 16, 2004

About a month from now, high school seniors across the country will find out whether they've gotten into college. Those fortunate enough to receive two or more acceptances will have to choose.

A decision may hinge on academics, financial aid or athletics, but for some students the most important factor will be fitting in.

Fish, of course, choose ''schools,'' too. And for a fish, fitting in can be all important. If it matches most of the others in size or behavior, it gains anonymity and protection from predators. But how does a fish choose the school that's right for it?

Scientists at the Universities of Leeds and Leicester in England have conducted experiments with three-spined sticklebacks that provide insight into their decisions.. The conclusion, reported in Biology Letters, a publication of the Royal Society, is that the fish gauge nearby fish, as well as the school as a whole.

The researchers set up an experimental tank, exposed a fish to two small schools, one on each side, and observed which it joined. The scientists found that if the schools consisted of fish of mixed lengths, the subject chose the school that had a majority of fish of its size. But if two other fish were placed between the subject and the schools, then the subject chose based on which nearby fish matched it in length.

In this way, the researchers say, fish use both local (the nearby fish) and global (the school as a whole) cues in assessing and choosing a school.

Really Small Mystery Balls

In centuries past in China, just about any ivory carver worth his salt could produce what is sometimes known as a mystery ball, a set of spheres within spheres laboriously carved from a single chunk of ivory. These adorned vases and other decorative items and, in the 19th century particularly, were often incorporated into chess pieces.

Researchers at the National College of Engineering in Caen, France, have produced something of a mystery ball of their own, though on an extremely small scale. They have synthesized a sphere of aluminum oxide molecules, with other cagelike structures of bismuth, strontium and oxygen in various combinations nested inside.

The outermost sphere consists of aluminum oxide tetrahedrons joined together in a pattern of hexagons and pentagons. To fans of R. Buckminster Fuller, this might sound familiar. His geodesic domes and spheres consisted of hexagons and pentagons.

In fact, the researchers report in the journal Nature Materials, their spheres resemble the geodesic spheres of carbon atoms that are known, in homage to Fuller, as fullerenes. The French team calls their new structures fullerenoid oxides.

The aluminum oxide molecules are arranged in such a way that they actually form two distinct layers, one of 84 aluminum atoms on the outside and another, just inside it, of 126 oxygen atoms. But there are four more structures within that, the innermost being a truncated tetrahedron of 12 oxygen atoms.

The researchers suggest that structures like these may eventually prove useful as molecular sieves or in catalysis or other applications.

Martian Moons in Motion

In addition to wandering across the landscape and probing rocks and soil for signs of water, the Mars rovers have been doing some moon watching. This month, the rover Opportunity photographed the smaller Martian moon, Deimos, as it passed in front of the Sun. That was the first time a spacecraft had photographed such a transit.

Opportunity and its twin, Discovery, photograph the Sun regularly to study the atmosphere's effects on sunlight. On March 4, the photograph was timed to coincide with the moon's transit. The camera also captured a view of the larger moon, Phobos, passing the edge of the Sun a few days later. Accurate timing of the transits may lead to a more accurate description of the moons' orbits.